[IntersectionObserver] #295 V2: visibility detection #523
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| : <dfn>isVisible</dfn> | ||
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| True if {{IntersectionObserver/trackVisibility}} is <code>true</code> | ||
| and the <a>visibility</a> algorithm, |
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This implies the value false if trackVisibility is false, while later on the algorithm is specified to immediately returns true in that case. Of the two, false has a safer failure mode if someone thinks they're tracking visibility but they screwed up somewhere. Either way, the two parts of the spec need to agree.
Even better would be if isVisible were completely undefined if you had not enabled trackVisibility.
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For the purpose of feature detection, how about setting isVisible to null if trackVisibility is false? I think that's also more consistent with other IDL I have seen.
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you can't set a boolean to null, can you? Honest question -- I'm not sure what the WebIDL can express, nor what would be most consistent with similar APIs. This feels kind of off, but a permanent false when tracking isn't enabled wouldn't be terrible. The true specified in the algorithm below will lead to trouble.
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I'm not an IDL expert, but for the record chromium's IDL code generator allows null-able booleans. I wrote a chromium patch which would implement the behavior I proposed, and it works.
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You can have nullable booleans (the IDL of this PR does not do that btw), but generally it would be better to use an enum.
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I'm not sure an enum will work here, because we need two different values that will evaluate to false when cast to boolean.
If there are no objections, I'll just make it a permanent false when tracking isn't enabled. I think that's probably what we want from a developer ergonomics no-surprises point of view. Feature detection can always be done via IntersectionObserverEntry.prototype.hasOwnProperty('isVisible').
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Update the PR based on comments so far, PTAL. |
SHA: 027e2dd Reason: push, by szager-chromium Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
`intersection-observer-v2`: spec merged into the Intersection Observer spec w3c/browser-specs#1210 w3c/IntersectionObserver#523 Co-authored-by: Daniel D. Beck <daniel@ddbeck.com>
The V2 set of features adds visibility reporting, with detection of occlusion and visual effects (explainer, issue).
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